Arc-control mechanism for projectors.



J. L. HALL.

ARG CONTROL MECHANISM FOR PROJEGTORS.

APXDLTGAMON FILED MA R.20 1908.

1,101,629, Patented June 30,1914.

4 SHEETS-SHEET 1.

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J. L. HALL.

ARC CONTROL MEGHANIBM FOR IROJEGTORS.

APPLICATION FILED MAR. 20, 1908. l

' Patented June 30, 1914.

4 SHEETS-SHEET 2.

John LHal by Wimesses:

J. L. HALL.

ARG CONTROL MEGHANISM FOR PROJECTORS.

APPLICATION FILED MAR.20,1908. Y

Patented June 30, 1914 4 SHEETSASHBET 3.

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J. L. HALL.

ARC CoNTRoL MBCHANISM'POR PROJEGTORS.

APPLICATION FILED MARZO, 1908. Patented June 30, 1914.

4 SHEETS`SHEET 4.

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L/o/m L, /f/d j anism for Projectors, of which the :followi `UNrrnnSTATES PATENT ornren JOHN' L. HALL, OFXSCHAENEOTADY,`NEW YORK', ASSIGNORT0 GENERAL ELECTRIC COMPANY, CORPORATION OF NEW YORK.

Anc-emmen MECHANISM ron Pnomorons.

Specification of Letters Patent. Application filed March 20, 1908.Serial No. 422,253.

Patented June 30, 1914.

To all wlw/ml it may concern.'

zen of the United States, residing at Schenectady, in the county ofSchenectady, State of New York, have invented'certain new and usefulImprovements in Arc-Control Meching is a. specification.

My invention relates to yarc controlling mechanism, and moreparticularly 'to the mechanism by whichthe length and position of thearc is controlled in searchlights,

projectors and similar devices in which an arc is used as a source oflight. l

The arc control mechanism for projectors heretofore used has usuallybeen provided with an automatic feeding device which can advance theelectrodes toward each other after the arc is established or struck bymeans of a series magnet, and thereby diminish the gap between them tocompensate for the consumption of the carbone while burning, but whichis unable to feed the electrodes through varying small amounts andthereby I increase the gap between them to compensate for arc changes.

. In large projectors and similar devices, espel cially wherelargecarbon electrodes are used the arc current and volts vary depending onthe crater formation and carbon texture and cause a sudden decrease aswell as increase of the arc drop, making it desirable Vvto automaticallyincrease as well as decrease the arc length `to'maintain constantcondition and even illumination.

` The object of my invention is to provide a control mechanism for thearc which will automatically, accurately and rapidly either increaseordiminish the gap between the electrodes and thereby maintain aconstant arc condition; which in searchlights will, by feeding bothcarbons or electrodes, maintain the arc in approximately the sameposition during their consumption, and which j is in generalanimprovement in the construction and operation of arc control mechanism,particularly Yfor searchlights and proj ectors.

rapid and exact, and b ro rl ro ortioning the feed of the iwb) csiboiisrto Ldorrespond tothe relative sizes of the two carbons the arcwill be maintained in approximately thefocus of the lens or mirror. Theadjustment of the gap between the `electrodes to maintain'the arc lengthconstant is preferabl controlled by some automatic regulating evicewhich responds to variations in potential between the electrodes. Such a.regulating device may assume many different forms, but in the preferredarrangement some suitable motor or driving mechamsm 1s arranged to moveone or both electrodes either to increase or diminish the gap betweenthe electrodes, and is controlled by a relay orA pilot device whichdetermines both lthe direction and extent of movement required to keethe arc length constant. The relay is ma e very sensitive and isconnected so that in one position it causes the e in the form of anelectromagnet, is made responsive to potential between the electrodes bybeing connected in parallel with them, and controls the drivingmechanism in any suitable way, preferably by means of a lockingmechanism which instantly and positively stops and holds the drivingmechanism and instantly releases it so that the driving mechanism startswithout delay and is instantly stopped without overrunning.

The relay is preferably, though not necessarily, provided with a seriescoil connected in series with the arc and wound to oppose the shuntcoil, which is connected in parallel with the arc. By using a sensitiverelay to control a powerful motor or driving mechanism directlyconnected across the line a very quick, powerful and accurate adjustmentof the length of the gap between the .electrodes is secured, even thoughthe adjustment requires a large and heavy electrode to be quickly movedin either direction.

vMy invention will best be understood in connection with theaccompanying drawings, which show one of the many forms in which it maybe embodied and in which` Figure 1 is a diagrammatic view show- 11o ingthe relation of the regulating and feed- I ing mechanisms to theelectrodes; Fig. 2 iS. a side view of a projector embodying my inventionwith the electrode supports shown in dotted lines; Fig. 3 is a plan viewof the framework for guiding the electrode sup` ports, said frameworkcontaining electrodeactuating mechanism of a form built and in use; Fig.4 is a vertical longitudinal section of the construction shown in Fig.3, with the actuating mechanism shown in elevation; andFig. 5 is an endview of the construction shown in Fig. 3, with the ratchets and pawlsfor actuating the feed screws shown in elevation.

In the specific. form shown in the drawings for purposes ofillustration, the arc is drawn between electrodes 1 and 2, mounted onand carried by suitable supports or holders 3 and 4, which are bothmoved by `any suitable actuating mechanism responsive to voltage acrossthe arc to increase or diminish the gap between the electrodes andthereby maintain the arc length constant. The supports or holders may bemade movable inany desired manner, preferably by mounting them oncarriages 5 and 6, which slide on guides in a I framework and are movedtoward and away from each other by any suitable feeding mechanism whichforms part of the actuating mechanism for the electrodes. In theparticular construction shown in the drawing, the carriage 5 is providedat each end with grooved wheels' 5a which run upon guide rails 5b. Theelectrode support 3 is` rigidly secured to the carriage 5, but isinsulated from it by insulation 5, while current is delivered to theelectrode support 3 and the electrode 1 through a flexible U- shapedconnection 3, formed of a plurality of thin strips of copper each withone end secured to the support 3, while the other end is secured to aflat bar 3b connected to one lead of the circuit which supplies currentto the projector. The other carriage 6 is provided with grooved wheels6a which run upon suitably shaped guide rails 6b and the electrodesupport 4 is mechanically secured to'the carriage but insulated from itby means of insulation 6C. Current is supplied to the electrode support4 through a flexible connection 4 'made of flexible strips ofcopper eachconnected at one end to the electrode support 4 and at the other end tothe `bar 4b, which in turn is connected to the vertical bar 4c to whichcurrent is supplied from y the other lead of the supply circuit throughconnections hereinafter described. The form of feeding mechanism shownin the drawings consists of a feed screw 7 engaging a nut 5d on thecarriage 5 and a feed screw 8 engaging a nut Gd on the carriage (i, thetwo feed screws being geared together through Gearing 9 and 10 soproportioned that the lectrodes are fed toward each other at such a ratethat the arc remains in practically the same position,,notwithstandingthe fact that one electrode is consumed more rapidly and is considerablylarger than the other.

The actuating mechanism for increasing and diminishing the gap betweenthe electrodes also comprises in addition to the carriages and feedscrews above described some kind of a motor or actuating device forrotating the feed screws in one direction or the other to cause the twoelectrodes to approach or to recede from each other. Any motor ordriving mechanism by means of which the feed screws may be rotated ineither direction fis suitable for this purpose, but the preferred formof actuating mechanism or motor is that shown in the drawings, in whicha ratchet wheel 11 mounted on the feed screw 8 is engaged by a pawl 12and isyrotated in one direction when the pawl is actuated, and is alsoengaged by another pawl 13 by which it may be rotated in the otherdirection. The pawls 12 and 13 are actuated by suitable connections 14and 15, shown diagrammatically in Fig. 1 as bell crank levers, and whichin the specific form shown in the other figures lare projections or lugson pivoted armatures 16 and 17 moved by means of an actuating magnet 18connected directly across the supply circuit and thereby subjected tothe full difference of potential on the supply circuit. The circuit ofthe magnet 18 is'broken at two gaps comprising rigid contacts 19 and 20arranged, as shown in Fig. 1, so that the closure of either gapcompletes the circuit through the electromagnet, while the armatures 16and 17 extend beyond theirvpivots and carry yielding contacts 21 and 22,which engage the contacts 19 and 2O when the armatures are drawn awayfrom the magnet by a spring 23, and thereby complete the circuit andenergize the magnet 18. The contacts for controlling the circuit of theelectromagnet 18 ymay be made in various ways but are preferablyconstructed as shown 1n the drawing, in which the yieldin contacts 21and 22 are in the form of U-s apcd spring blades secured to thearmatures in a position to engage the rigidcontacts 19 and 20. As yyielding contact will be drawn away from the stationary contact as thearmature is attracted into engagement with the electromagnet 18. Asshown in Fig. 1, each armature completes the circuit of theelectromagnet and energizes it when the armature is drawn away from themagnet by the spring,

While the' movement of the arma-ture into the armature drops back to itsoriginal position. Eitherof the armatures 1-6 or 17 will',

- if unrestrained", vibrate rapidly and strongly aslong'astlieelectromagnet 18 is connected to the circuit. y

The mechanism above described constitutes the motor part of anactuatingmechanis'm for the electrodes, in which the vibration 'of thearmature 16 will actuate the ratchet wheel 11 andthe feed screws 7 and 8and cause the electrodes 1S and 2 to approach each' other and the gapbetween them, while the vibration of the other armature will drive theratchet wheel 11 in the reverse direction and causethe electrodes tomove apart and increase the gap between them. Since both electrodes aremovable and the armatures 16 'and- 17 .vibrate with strong impulses andat high speed when they are unrestrained, the adjustment of theelectrodes with relation to each other isl accomplished very quickly andthe length of the arc remains substantially constant;

In' order to secure the best results the actuating mechanism forcontrolling the gap between'the electrodes should"D automaticallyrespond to' variations in the potential between the electrodes tomaintain the length ofthe arc and the differente of potential betweentheelectrodes constant. In the projectors heretofore used, a shunt coil,connected in parallel with the arc was arranged toA feed the electrodestoward each other as the gapbetween the electrodes became too great, buthad the disadvantage of not providing any means for increasing the gapbetween the electrodes in case the arc became too short,A and also thedisadvantage that a very sensitive coil did not have suliicient power tooperate the electrodes satisfactorily; while a coil powerful enough tomove the electrodes quickly was not suliciently sensitive to variationsin voltage. Where large electrodes are used the variation in the arccharacteristics may make a very considerable difference in thedifference of-potential between the electrodes, and if the arc is to bemaintained at constant length, the gap between the electrodes must beeither increased or decreased very quickly by some comparativelypowerful actuating mechanism, which moves one or both of the electrodes.In my invention this result is attained by making the motor or drivingmechanism for moving one or both of the electrodes as powerful, as maybe necessary, and the entire actuating mechanism for controlling the gapbetween the electrodes is made responsive to variations of the potentialbetween the electrodes by the use of arelay, or similar selectivedevice, which is responsive to said variations and controls the Amotoror driving mechanism in any suitable manner, preferably mechanicallythrough some locking device or mechanism which will instantly releasethe driving mechanism' and permit it to run and will instantly andpositively stop and Vhold it in any desired position, thereby avoidingthe use of electrical contacts which may become oxidized.' Since thework the relay 's called upon to dois very light it may be ade assensitive as desired and may be made in many dilierent" forms andconnected in varousl ways so long as it is responsive to the variationsin arc length. The preferred arrangement, as shown in the drawings, isone in which, between the regulating resistance 24 and the electrode l,a relay magnet comprising a shunt coil 25 is connected across thecircuit in parallel with the electrodes 1 and 2'. Itis preferable butnot necessary to connect in series with thearc, a series coil 26differentially wound as regards the shunt coil 25, and mounted upon acore 27 common to both coils so thatthe magnetization ,-0 of the core 27of the relay or pilot -magnet a depends on boththe shunt current due tothe difference of potential between the electrodes 1' and 2, and alsowith the currentflowing between the electrdes and depends 9 on thealgebraic sum of the two excitations ca-used by said currents. In thespecific arrangement shown in the drawings, the series coil 26 isconnected in series with the electrode support 4 by means of connec- 100tion bar 26- which joins one end ofthe series coil to the bar 4c and bymeans of a curved connection bar` 26", which joins the other end of theseries coil to a flat bar or lead 26, which in turnisl connected -to a105 binding post by 'means of which one of the leads of the supplycircuit may be secured to the projector. In theoperation of the devicethe current l'ows from one lead of the supply circuit to the Hat bar 3b,thence 110 through the flexible U-shaped connector 3a to the electrodesupport 3 and electrode l, I y thence through the arc` to the electrode2, through the electro-de support 4 and the flexible connector la toconnector bars 4" 115 and 4, thence through the conductor 26a, seriescoil 26, U-shaped connection 2Gb, and

the connecting bar 26c to the other lead of the supply circuit.

The relay or pilot magnet may control the motor or driving mechanism forone or both electrodes by means of any suitable locking or controllingmechanism; buta form of control particularly adapted to the control ofthe. driving mechanism illustrated in the drawings comprises anarmature28 responsive to the relay or pilot magnet, and connected to apivoted latch or detent 29, which normally, under the influence oflgravity, or of a spring, tends to engage the armature 16 130 andlholdit -against the magnet 18 in the inoperative position shown in Fig. 1.At the other end of the relay -magnet a correspondingv armature 30 isconnected to a pivoted latch 3l, controlled by a spring 32 normallytending to move the armature 30 away from the relay magnet and to movethe latch 31 into the position lshown in Fig. 1, where the armature 17is freetovibrate under the in.- fluence of the spring 23land of themagnet 18.

fmovement; but if the potential between the.

The various parts are so proportioned that when the current through therelay magnet is normal, both ldetents 29 and 31 restrain the twoarmatures 16 and 17 Aagainst electrodes varies and consequently. theeurrent increases above, or decreases below its -normal value, `therelay and its armatures respond to the variations of potential, and oneor the other of the detents ismoved v and releases its armature, whichthereupon begins to vibrate and the necessary adjustment in the gapbetween the electrodes 1 and 2 is made very quickly and accurately.A Thedriving mechanism always tends or is biased to operate the adjustingmechanism as' long as there vis a difference of potential f on thesupplyleads of the projector and consequently the driving mechanismbegins to act the instant the detent is lifted and the mechanism lisfree.

Owing to the comparaf tively" lightweight of the moving parts ascomparedA with the force vexerted by theb electronviagnet 18 there ispractically no inertiafor time lag in starting the mechanism and on theother hand it is stopped instantly and inthe exact' position desiredwhen one or the other of the detents 29 or 31' drops into lockingposition and holds the corre- `a-sponding armature immovable. As aresultof this construction, the tendency ofthe driving mechanism to overrunand move theelectrode support beyond the desired position is overcomeand theA adjustment of the,

electrodes is made much more accurately j and quickly than'where a motoror similar device having considerable inertia is used as the drivingmechanism.

The operation of the device is -as follows: If it be assumed that withthe parts in the position shown in Fig. 1 the electrodes 1 and 2 are tooclose together, then the resist ance between them is below the normal,and as a result the amount' of current flowing through the shunt coil 25'is considerably The slight increase in".

that`the relay magnet is unable to hol the 17 into the position shown inFig. 1, thereby causing the bridging contact 22 to close the' circuit ofthe magnet 18 through the gap formed between two stationary contacts`20. As soon as this occurs the magnet 18 issubjccted to the fullpotential of the supply circuit across the line, and the armature 17begins to vibrate rapidly, making and breaking the circuit of the ma et18, and at the same 4time vibrating the ellcrank lever 15 and the pawl13, and causing a rotation in one direction of the feed screws 8 and 7.The rotation of the feed screws moves the electrode holders 3 and 4 andcauses a separation of the electrodes and a corresponding increase inthe gap between them. As a result of the increase in the gap theresistance of the arc and the,

difference of potential between the electrodes increase, causing moreand more current to flow through the shunt coil 25. The mechamsm.continues to operate and to increase .the gap between the electrodesuntil 'the current through the shunt coil 25 reaches such a value thatthe relay magnet is enabled to draw the armature'. 30 down against thespring 32, and .thereby bring the detent 31 into the positionto-engageand hold the armature l17 against themagnet 18 and restrain it fromfurther movement, As vthe are continuesl to burn the carbons waste away,and eventually the length of the arc vand the diference of potentialbetween'the electrodes become greater than normal. When this occurs acurrent greater than normal is flowing through the shunt coil 25,

energizing the relay magnet to a,y point where it is enabled to piek uthe armature 28 and thereby lift the etent 29 out of engagement with thearmature 16. When this occurs the spring 23 -draws the` armature 1G awayfrom the magnet`18, and simultaneously closes the circuit of the mag#net through the gap formed between stationary contacts 19, whereupon thearmaturex 16 begins to-vibrate and moves and. actuates through the bellcrank 14 and pawl 12, and thereby drives the feed screw 8 and the feedscrew 7 in the reverse direction.

The movement of the feed screws in the reverse-direction shiftsthesupports 3. and 4,

and lcauses the electrodes land 2- to preach each otherA andcorrespondingly iminish the gap Abetween them. The vibration of thearmature 16 continues until the arc length and the differenceofpotential between the electrodes 1 and 2 becomes normal, Awhereupon thecurrent through the lshunt coil 25 diminishes to such a oint armature 28and the detent 29 out of the locking position, so that the armature anddetent drop and lock the armature 16 in the inoperative position shownin Fig. 1. These operations are repeated as the length of the i arefluctuates on each side of the normal, and since the relay or pilotmagnet is sensitive, and the motor or driving mechanism is powerful, therequired adjustment of the gap between the electrodes is made veryquickly, and the length of the arc remains substantially constant duringthe operation of the device.

My invention may be vembodied in many other forms than that shown anddescribed, and I, therefore, do not wish to be' restricted to theprecise form disclosed, but intend to'cover by the appended claims allchanges and modifications within the spirit or scope of my invention.

What I claim as new 'and desire to secure by Letters Patent of theUnited States, is,-

1. In an arc control mechanism, the combination with electrodes movablein two directions to vary the arc lbetween them, of electricallycontrolled step-by-step mechanisms comprising two pawls and a commonratchet for Inoving said electrodes one pawl for moving them in onedirection and the other for moving them in the other direction, andelectrically controlled means for locking lsaid mechanisms againstmovement in either or both directions.

2. InA an arc control mechanism, the combination with a movable supportfor an electrode, of an actuatingelectromagnet having two pivotedarmatures, 'each arranged to make'and break the circuit of saidelectromagnet, feed mechanism for said support actuated by one armatureto increase and by /the other armature to decrease the gap between theelectrodes, and means responsive to variations of potential between theelectrodes for locking either or both of said armatures againstmovement.

3. In an arc control mechanism, the combination with a movable supportfor 'an elec- 'cuit when in operation, a locking device for positivelyholding said member stationary in circuit opening position andelectroresponsive means connected to said locking device to control saidmovable member.

4. In an arc control mechanism, the combination with movable supportsfor a pair of electrodes, of electro-responsive actuating mechanismpermanently connected to the supply leads and comprising a pair ofmovable members either of which is adapted to close the circuit of saidmechanism and to periodically open the same when-in operation, lockingdevices cooperating with said members to positively hold the samestationary in circuit-opening position, and electroresponsive means forselectively releasing said locking devices.

5. In an arc control mechanism, the combination with movable supportsfor a pair of electrodes, of electro-responsive actuating -mechanismpermanently connected to the supply leads and comprising a pair ofmovable members either of which is adapted to close the circuit of saidmechanism and to periodically open the same when in operation, and meansfor locking said movable members and for selectivelyv releasing the samecomprising an electro-magnet and two cop'erating armatures for operatingthe respective locks.

In witness whereof, I have hereunto set my hand this 19th day of March,1908.

. JOHN L. HALL.

Witnesses:

HELEN ORFORD, BENJAMIN B.. HULL.

